Generally, strategies for combating tsunamis, floods, and other water-related disasters have centered on local authorities. In the case of tsunamis, for example, massive breakwaters are built to prepare for a tsunami onset, or, when a tsunami warning has been issued, instructions to make swift evacuation to higher ground are issued.
However, massive breakwaters were broken by the unexpected major tsunami produced by the Great East Japan Earthquake, failing to stop the approach of the tsunami and leading to numerous deaths. Individuals who evacuated to higher ground at the time survived. First evacuating to higher ground is of utmost importance and a fundamental part of surviving a disaster. However, even when there are designated tsunami evacuation sites, these are often located at natural high ground. Due to the natural topography, it may take effort to reach these evacuation sites, which are not necessarily easy to utilize. Wheelchair users, the elderly, children, and other socially disadvantaged individuals experience particular difficulties.
For this reason, various types of tsunami evacuation facilities have been proposed that can be used without hesitation during an emergency, yield the same effects as evacuation to higher ground even without having to actually climb to higher ground, and can be safely used by the socially disadvantaged as described above.
For example, there has been proposed a facility that can be used for keeping pets or as a garage during normal circumstances, while allowing even children and the elderly to reliably evacuate during a tsunami or flood (see Patent Document 1). This facility is moored to the ground by a link, whereby the facility returns to its original position without drifting when the water ebbs. The facility functions as a disaster preventive shelter into which people retreat during a tsunami or flood, the shelter floating when the surrounding area is filled with water to improve the safety of disaster victims.
There has additionally been proposed a base-isolated construction for avoiding flood damage in which a building does not flood during high-tide flooding (see Patent Document 2). This construction is provided with a foundation having an open upper surface and comprising side walls and a bottom surface, a floating body is accommodated inside the foundation, and the building is constructed on the floating body. Provided are transmission means for cushioning and transmitting the vibration of an earthquake and a damper for limiting the amplitude of the vibrations are provided between the floating body and the building; as well as an anchor pole formed integrally with the floating body and extending/retracting below the floating body, and a locking member on the foundation bottom surface that locks integrally with the foundation. The anchor pole and locking member are configured to engage and integrate, and the floating body raises and lowers the anchor pole during flooding so that the building does not flood.
There has also been proposed a disaster preventive shelter structured to improve the safety of disaster victims during a tsunami or flood (see Patent Document 3). This disaster preventive shelter has a hollow structure of substantially spherical shape comprising a watertight interior space, and is provided with an entrance that can be closed in a watertight state by opening/closing doors, the bottom part of the hollow structure being provided with a mass for balance. During a disaster, the disaster preventive shelter floats on the water while people are accommodated in the interior space.
There has additionally been proposed a tsunami shelter apparatus for improving safety and saving many trapped disaster victims as a tsunami evacuation facility that floats but is not washed away (see Patent Document 4). The body of this tsunami shelter evacuation facility comprises a hemispherical evacuation chamber in the upper part and a hemispherical flotation chamber in the lower part, the bottom-most part of the flotation chamber being linked to foundation ground by a tethering cable. This allows the tsunami shelter apparatus to float while remaining connected to the ground by the tethering cable, and suppresses shaking.